This cart goes by the long name of: "TMS CART-CANOE/KAYAK-KY001 New Jon Boat Kayak Canoe Carrier Dolly Trailer Tote Trolley Transport Cart Wheel." At least, that's what it's called on Amazon.com, where I ordered it.
It looks like a lot of other kayak carts -- hollow metal tubing, fat black tires, foam cushioning. But there's a huge difference. I got this one for about $35 -- under $22 for the cart, and under $13 for shipping and handling! AND, it works just fine. I used it to wheel my kayak down a fairly steep hillside from a parking lot to the drought-receding lake, across ruts and grass and then lots of sand, with no problem.
Word of warning, this is cheap for a reason -- made in China, in fact. And the rubber of the tires smells Terrible. Take my word; open the box outside, and don't leave the cart in your car for any longer than you have to until that new rubber smell fades. Other than that, though, it's a great solution for those of us who have to portage our own kayaks by ourselves.